1. Field of the Invention
The invention relates generally to communication systems and in particular to radio frequency (RF) architectures.
2. Discussion of the Related Art
The Institute of Electrical and Electronics Engineers (IEEE) formed the IEEE 802.22 Working Group to develop protocols for an interoperable air interface for use in spectrums allocated to TV broadcast service and to provide wireless services, such as broadband access, a point-to-multipoint wireless regional area network (WRAN). IEEE 802.22 specifies that a network should operate in a point-to-multipoint (P2MP) basis. A system should be formed by base stations (BSs) and customer premise equipment (CPE). The CPEs are attached to the BSs via wireless links in a specified frequency range. Each BS controls the medium access for all CPEs attached to it.
Currently, co-channel inter-BS communication using co-existence beaconing protocol (CBP) is the state of the art. FIG. 1 is directed towards a related art communication between BSs of multiple neighboring WRAN cells that are operating on the same channel. Referring to FIG. 1, the system is illustrated generally as reference number 100. As shown in FIG. 1, a WRAN1 102 and WRAN2 104 are operating on the same channel. There are multiple frames n to n+3 in which data from WRAN1 102 and data from WRAN2 104 can be transmitted. At the end of every data frame, WRAN1 102 and WRAN2 104 schedule a contention-based (i.e. carrier sense media access (CSMA) protocol based) co-existence window (CW) 110 in which co-existence beacon (CB) packets 112 can be transmitted and received. In operation, WRAN1 102 and WRAN2 104 need to co-exist with each in order to avoid operating on the same channel as neighbors and licensing incumbents.
When data frames of WRAN cells are synchronized on all operating channels as shown in FIG. 1 and the CWs 110 are synchronized among WRAN1 102 and WRAN2 104, the WRAN cells can transmit or receive CB packets 112 during the synchronized CWs 110 using best effort, contention-based protocols so as to communicate with one another. Best effort, contention-based protocols are known to one of ordinary skill in the art and include, for example, those described in IEEE 802.22 Draft Standard version 0.1, document number 22-06-0068-00-0000, which is incorporated by reference. In operation, WRAN1 102 and WRAN2 104 can communicate with each other over the CWs 110 at the end of each frame as all the frames are synchronized. More specifically, if WRAN1 102 is transmitting and WRAN2 104 is receiving, communication would be successful.
However, there is also a need to communicate among neighboring WRAN cells that are operating on different channels for exchanging co-existence information. The need to communicate among neighboring cells includes, for example, communicating for sensing quiet period coordination and spectrum sharing coordination, among other needs. FIG. 2 illustrates a related art communication between BSs of multiple neighboring WRAN cells that are operating on different channels. Referring to FIG. 2, the system is illustrated generally as reference number 200. The system 200 includes a WRAN1 202 and WRAN2 204 operating on different channels as identified by the hatching and non-hatching patterns.
The system is similar to the single-channel CBP operation of FIG. 1 in that there are multiple frames n to n+3 in which data from WRAN1 202 and data from WRAN2 204 can be transmitted to each other. This communication occurs as each WRAN cell (202 and 204) schedules a CW 210 at the end of every data frame in which CB packets 212 can be transmitted and received. More specifically, in communication of WRAN1 202 and WRAN2 204 during a CW 210, each WRAN cell can either stay on its own operating channel or tune to another channel occupied by a neighboring WRAN cell. For example, WRAN1 202 can tune to either channel 214 illustrated by a non-hatching pattern or channel 216 illustrated by a cross-hatching pattern during a CW 210.
It is apparent from FIG. 2 that the communications between two neighboring WRAN cells can succeed only when these two cells are tuned to the same channel during a CW 210. In addition, communication will only succeed when one of the WRAN cells is transmitting and the other is receiving. This is illustrated as CB packets 212 are exchanged when the CW 210 of neighboring WRAN1 202 and WRAN2 204 are on the same communication channel 216. There is a problem with multi-channel inter-WRAN communication when the cells are on different channels or when the transmitting and receiving of the WRAN cells are not coordinated, that is, no communication is received as indicated by reference 218. This leads to poor efficiency of co-existence communications among multiple neighboring WRAN cells that operate on different channels. Accordingly, coordination of CB communications ensures the success of multi-channel inter-WRAN communication using CBP.